This volume is intended to complete the Cell Chemistry and physiology module. It is about how the traditional boundaries of cell chemistry and physiology are being erased by molecular biology. We do not think it necessary to elaborate on this theme, particularly since the body of core knowledge found in this volume brings us a stage closer to answering the question, "what makes cell biology into a new discipline?" The first part of the volume deals with the chemistry of actin and myosin and is followed by chapters on cell motility, ATP synthesis in muscle, and contraction in smooth and skeletal muscle. Here the reader is immediately made aware of the contributions molecular biology is making to our understanding of the molecular mechanisms underlying muscle contraction. It is perhaps enough to point out that Huxley's concept of the cross-bridge cycle and generation of force can now be explained in molecular terms. Topics such as muscle fatigue and muscle disorders, as well as malignant hyperthermia are bound to arouse active learning in the student and set the stage for problem-based learning. Most medical students look askance at thermobiology. We think this is a mistake; hence, we have included a section dealing with this subject. This brings us to the chapter on the heat shock response, which at the very outset makes clear that many stressors besides heat are known to result in heat shock gene expression. Many of the heat shock proteins occur in unstressed cells and some of them behave as chaperones. These proteins also reach high levels in a wide range of diseases including neurodegenerative disorders. Whether certain diseases are the result of mutations in the heat shock genes is not yet known. As will be appreciated, much of the work done in this field involved the use of cultured cells. Animal cells in culture are the subject of the last chapter.